The invention relates generally to solid-state photomultipliers, and more particularly to techniques for improving timing performance of solid-state photomultipliers.
A solid-state photomultiplier (SSPM) is a photosensor consisting of an array of photodiodes that are connected in parallel and operated above their breakdown voltage in so-called Geiger mode. SSPMs provide many advantages over conventional photomultiplier tubes (PMTs) and are therefore being used in many applications. These advantages include better photon detection efficiency (high probability of detecting an impinging photon), compactness, ruggedness, low operational voltage, insensitivity to magnetic fields and low cost.
However, current SSPMs generally have slower single-photon response. Even though they may have significantly higher photon detection efficiency than do PMTs (˜50% vs. 25%), SSPMs generally have inferior timing resolution compared to fast PMTs. In a standard SSPM, the single-photon response (i.e. impulse response) is approximated by an exponential function, with the decay time given by the RC time constant of the quenching resistor and the diode capacitance. Since these time constants are usually on the order of tens to hundreds of nanoseconds, the single-photon response of an SSPM is much slower than the single-photon response of a PMT designed for timing applications. Thus, for applications that require precise timing measurements, such as time-of-flight PET, SSPMs have potential limitations.
It is therefore desirable to provide an efficient SSPM with improved timing resolution.